The following non-IEOR courses are highly recommended for students
seriously interested in PhD in operations research. These can be taken 
toward PhD minors in EECS, Math, Statistics, Economics, Civil & Env Engineering.

EECS Courses

CS170  Efficient Algorithms and Intractable Problems 
CS172  Computability and Complexity
CS174  Combinatorics and Discrete Probability
CS270  Combinatorial Algorithms and Data Structures
CS271  Randomness and Computation
CS276  Number Theory and Cryptography 
CS277  Concrete Complexity  
CS278  Machine-Based Complexity Theory 
CS282  Algebraic Algorithms
EE227A Introduction to Convex Optimization
EE227B Convex Optimization and Approximation

Math Courses

MATH 104  Introduction to Analysis
MATH 105  Second Course in Analysis
MATH 110  Linear Algebra
MATH 113  Introduction to Abstract Algebra
MATH 170  Introduction to Optimization
MATH 172  Combinatorics
MATH 220  Methods of Applied Mathematics
MATH 221  Advanced Matrix Computations
MATH 249  Algebraic Combinatorics
MATH 250A Groups, Rings, and Fields
MATH 250B Multilinear Algebra and Further Topics

Statistics Courses

STAT200A-200B  Introduction to Probability and Statistics at an Advanced Level
STAT205A-205B  Probability Theory
STAT206A-206B  Stochastic Processes
STAT232  Experimental Design
STAT238  Bayesian Statistics
STAT230A Linear Models

Econ Courses

ECON201A-201B  Economic Theory
ECON202A-202B  Macroeconomic Theory
ECON207A-207B  Mathematical Economics
ECON206        Mechanism Design and Agency Theory

Civil & Environmental Engineering Courses

CEE251  Operation of Transportation Facilities
CEE258  Logistics

See  UC Berkeley course catalog  for more.